The surface of silk is modified by a cationic reagent, N-(3-chloro-2-hydroxypropyl) trimethylammonium chloride(CHTAC) in order to enable the fibre to be dyed with superfine pigments by an exhaust process. The effects of cationization pretreatment conditions such as the amount of cationic reagent, pH, treatment temperature and time on color yield are discussed in detail. The result shows that the condition suitable for modification treatment is that the concentrationc of cationic reagent is 10g/l, pH 8, liquor to goods ratio of 100:1 and $60^{circ}C$ for 30 min. The white index decreases with the increase of alkali of cationic treatment. The crock fastness and wash fastness of silk dyed by pigment exhaust dyeing achieve 3-4 and 4 scale, respectively. The treated silk fabrics still retain a soft handle because the bending rigidity B and hysteresis 2HB increase slightly after cationization pretreatment and dyeing procedure. It has been demonstrated that properties of surface modified silk dyed with superfine pigment by exhaust process are acceptable.